8.18. UniqueProcess

The UniqueProcess is optimized for GeoMesa to find unique attributes values for a feature collection, which are returned as a json object. It accepts the following parameters:

Parameter	Description
features	The layer to query
attribute	The attribute for which unique values will be extracted
filter	A filter to apply to the feature collection
histogram	A Boolean to enable returning a histogram of attribute values, instead of just a count of the total unique values
sort	Sort the results; allowed values are ASC or DESC
sortByCount	A Boolean to enable sorting by histogram counts instead of attribute values
output	The output feature collection encoding

8.18.1. Unique Example

The following XML is an example of a UniqueProcess that reports the unique names in in the ‘Who’ field of a layer over a restricted bounding box (-77.5, -37.5, -76.5, -36.5):

<?xml version="1.0" encoding="UTF-8"?>
<wps:Execute version="1.0.0"
    service="WPS"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://www.opengis.net/wps/1.0.0"
    xmlns:wfs="http://www.opengis.net/wfs"
    xmlns:wps="http://www.opengis.net/wps/1.0.0"
    xmlns:ows="http://www.opengis.net/ows/1.1"
    xmlns:xlink="http://www.w3.org/1999/xlink"
    xsi:schemaLocation="http://www.opengis.net/wps/1.0.0 http://schemas.opengis.net/wps/1.0.0/wpsAll.xsd">
  <ows:Identifier>geomesa:Unique</ows:Identifier>
  <wps:DataInputs>
    <wps:Input>
      <ows:Identifier>features</ows:Identifier>
      <wps:Reference mimeType="text/xml" xlink:href="http://geoserver/wfs" method="POST">
        <wps:Body>
          <wfs:GetFeature service="WFS" version="1.0.0" outputFormat="GML2" xmlns:cite="http://www.opengeospatial.net/cite">
            <wfs:Query typeName="cite:AccumuloQuickStart"/>
          </wfs:GetFeature>
        </wps:Body>
      </wps:Reference>
    </wps:Input>
    <wps:Input>
      <ows:Identifier>attribute</ows:Identifier>
      <wps:Data>
        <wps:LiteralData>Who</wps:LiteralData>
      </wps:Data>
    </wps:Input>
    <wps:Input>
      <ows:Identifier>filter</ows:Identifier>
      <wps:Data>
        <wps:ComplexData mimeType="text/plain; subtype=cql"><![CDATA[BBOX(Where, -77.5, -37.5, -76.5, -36.5)]]></wps:ComplexData>
      </wps:Data>
    </wps:Input>
    <wps:Input>
      <ows:Identifier>histogram</ows:Identifier>
      <wps:Data>
        <wps:LiteralData>true</wps:LiteralData>
      </wps:Data>
    </wps:Input>
    <wps:Input>
      <ows:Identifier>sort</ows:Identifier>
      <wps:Data>
        <wps:LiteralData>ASC</wps:LiteralData>
      </wps:Data>
    </wps:Input>
    <wps:Input>
      <ows:Identifier>sortByCount</ows:Identifier>
      <wps:Data>
        <wps:LiteralData>false</wps:LiteralData>
      </wps:Data>
    </wps:Input>
  </wps:DataInputs>
  <wps:ResponseForm>
    <wps:RawDataOutput mimeType="application/json">
      <ows:Identifier>result</ows:Identifier>
    </wps:RawDataOutput>
  </wps:ResponseForm>
</wps:Execute>

Assuming the above XML is in a file named UniqueProcess_wps.xml, it can be invoked with the following curl to GeoServer:

curl -v -u admin:geoserver -H "Content-Type: text/xml" -d@UniqueProcess_wps.xml localhost:8080/geoserver/wps

The query should generate results that look like this:

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "value": "Addams",
        "count": 37
      },
      "id": "fid--21d4eb0_15b68e0e8ca_-7fd6"
    },
    {
      "type": "Feature",
      "properties": {
        "value": "Bierce",
        "count": 43
      },
      "id": "fid--21d4eb0_15b68e0e8ca_-7fd5"
    },
    {
      "type": "Feature",
      "properties": {
        "value": "Clemens",
        "count": 48
      },
      "id": "fid--21d4eb0_15b68e0e8ca_-7fd4"
    }
  ]
}